We have two outbound SIP proxies (Sonus SBC) and one of them is being used as a redundent server. We are facing a particular issue: if the main proxy fails, there is a long delay in establishing calls.
I have done some investigations and this is what happens:
1- The VVX phone (VVX 500 with UC version 5.2 or 5.4) uses DNS and gets two SRV records.
2- The first SRV record (lower priority) is used and phone tries to register to the main outbound proxy.
3- SIP registration fails so the phone uses the second SRV and registers.
4- When making a call, the phone still sends the SIP subcribe and invite messages to the main proxy which is out of service. Obviously the messages fail and after some retry the phone sends the request to the backup proxy.
Is this the intended behaviour for the SRV records? This is causing 5 seconds delay for the user just to hear the dial tone. Then another 7-8 seconds delay for the destination to be invited.
Is there a configuration that needs to be changed?
I have attached the SIP log file and phone configuration backup.